The branching fraction for the decay $K^{-} to pi^{0} e bar u$ is measured using in-flight decays detected with {bf ISTRA+} setup working at the 25 GeV negative secondary beam of the U-70 PS:linebreak $Br_{K_{e3}}= (5.124 pm 0.009 (stat) pm 0.029(no
rm) pm 0.030(syst))%$. From this value the $|V_{us}|$ element of the CKM matrix is extracted, using previously measured $f_{+}(t)$ form factor: $|V_{us}|=0.227 pm 0.002$. The results are in agreement with recent measurements by BNL E865, FNAL KTeV, KLOE.
